The present application is related to medical devices and methods for inhibiting restenosis in blood vessels. Specifically, the present invention is related to intravascular catheters utilizing a tubular member having a distally disposed radiation source over a core wire and methods of their use.
Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). These therapeutic techniques are well known in the art and typically involve use of a guide wire and a balloon catheter, possibly in combination with other intravascular devices. A typical balloon catheter has an elongate shaft with a balloon attached proximate to its distal end and a manifold attached to the proximal end. In use, the balloon catheter is advanced over the guide wire such that the balloon is positioned adjacent a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
Vascular restrictions that have been dilated do not always remain open. In approximately 30% of the cases, a restriction reappears over a period of months. The mechanism of this restenosis is not fully understood. The mechanism is believed to be different from the mechanism that caused the original stenosis. It is believed that rapid proliferation of vascular smooth muscle cells surrounding the dilated region may be involved. Restenosis may be in part a healing response to the dilation, including the formation of scar tissue.
Intravascular radiation, including thermal, light and radioactive radiation, has been proposed as a means to prevent or reduce the effects of restenosis. For example, U.S. Pat. No. 4,799,479 to Spears suggests that heating a dilated restriction may prevent gradual restenosis at the dilation site. In addition, U.S. Pat. No. 5,417,653 to Sahota et al. suggests that delivering relatively low energy light, following dilatation of a stenosis, may inhibit restenosis.
Delivery of radioactive radiation has been proposed as a means to prevent or reduce the effects of restenosis. Dake et al. suggest delivering radiation within the distal portion of a tubular catheter. Fischell, in the publication EPO 0 593 136 A1, suggests placing a thin wire having a radioactive tip near the site of vessel wall trauma for a limited time to prevent restenosis. Problems exist in attempting to provide uniform radiation exposure using a point or line source. Specifically, as the radiation varies inversely with the square of distance for a point source and inversely with distance for a line, a source laying off center near one vessel wall may significantly overexpose the nearby wall while underexposing the further away wall. This is especially critical for beta radiation which is absorbed by tissue and blood at a relatively short distance from the source.
Use of continuous centering balloons having a beta radiation source within has been suggested, but may allow the radiation source to xe2x80x9cwarpxe2x80x9d when placed across curved vessel regions, allowing the balloon to bend but having the central radiation source lying in a straight line between the two ends.
What remains to be provided is an improved apparatus and method for delivering uniform radiation to vessel interiors to inhibit restenosis.
The present invention includes a radiation source which can be used to inhibit restenosis of blood vessels, the source having a tubular radioactive distal region adapted to slide over a radiation source guide wire or core wire. In all embodiments, the radiation source guide wire or core wire extends within a lumen, sealed on its distal end over substantially the entire length of a delivery catheter (at least distally to a point within an expandable balloon). The core wire further extends out the proximal end of the delivery catheter a sufficient distance or length to thread the tube or radiation source thereon. One radiation source includes a tubular body having a lumen the entire tube length, which can be used with a radiation source guide wire extending proximally out of the proximal end of a delivery catheter for at least the length of the tube. Another source includes a tubular body having a lumen the entire tube length but having a first guide wire port on its distal end and a second guide wire exit port a short distance proximal of the distal end, allowing the use of a shorter radiation source guide wire extending proximally from the proximal end of the delivery catheter to thread the tube thereon. Yet another source includes a short radioactive, tubular distal member disposed at the end of a shaft with the short distal tubular member having a distal and proximal opening for threading over the radiation source guide wire, again allowing the use of a radiation source guide wire which extends a short distance proximally out the proximal end of the delivery catheter to thread the tubular radiation source lumen thereon. The tubular body could also be of a two-piece construction with the short distal radiation portion detachable from a long proximal segment.
Still another radiation source features an elongate tubular body having a short distal radioactive portion and a lumen the entire tube length and having a longitudinal slot extending through the tube wall over a portion of the length of the tubular body. The slot extends from the proximal end of the tubular body, where it is open to the lumen at the proximal end, to a point proximate the radioactive portion. The slotted embodiment allows a radiation source guide wire to be threaded by extending the wire radially through the slot, holding the core wire position constant, while advancing the tube into the catheter and patient, thereby threading the entire tube while requiring the core wire to extend proximally from the proximal end of the delivery catheter a short distance about equal to the non-slotted length of the tubular body.
The tubular body can be formed of Nitinol. In a preferred embodiment, the elongate tubular body having the distally disposed radioactive source includes a plurality of cutouts or openings through the tubular wall in a distal portion thereof. The plurality of cutouts, holes or slots extend around the circumference of the tubular body and over a portion of the lengths thereof, wherein the cutouts are in a selected pattern separated by bridges of the material of the tubular body. The cutouts provide added flexibility in the distal portion of the tubular body which much navigate a more tortuous path to be positioned within the expandable balloon of the delivery catheter in a prior stenosed region. The cutouts, holes or slots may be distributed in any selected pattern to impart such increased flexibility. A preferred pattern includes a generally spiral or helical pattern of cutouts having bridges extending longitudinally between cutouts every 120 degrees. Radiation sources according to the present invention can have radioactive material incorporated into the tubular material or secured to the surface of the tubular body. In preferred embodiments, the tubular member is made from Nitinol with a metallic radiation source plated onto a portion of the surface thereof.
The present invention includes an inflatable balloon delivery catheter having a closed end radiation delivery lumen and a radiation source guide wire or core wire within the lumen. In one catheter, the radiation delivery lumen can serve as the inflation lumen. Another catheter includes an inflation lumen separate from the radiation source delivery lumen. Another preferred embodiment of delivery catheter includes a separate radiation source lumen and a separate inflation lumen in combination with a single operator exchange guide wire lumen which doubles as a passive perfusion lumen during radiation treatment.
The tubular radiation source and delivery catheter can be used in conjunction with a radiation shield or vault and a transfer tube. The vault can shield the radiation source when the source is outside of the patient""s body. The transfer tube can be used to quickly transfer the radiation source from the vault into the delivery catheter. A preferred vault includes a path with multiple bends to shield the entrance and exit of the vault.
The tubular shape of the radiation source can provide a more even radiation exposure to vessel walls. In particular, due to the inverse square relationship between distance and radiation intensity, the tubular shape reduces the possibility for extreme under-exposure and over-exposure caused by a point or line radiation source becoming much closer to one side of a vessel than the other. The tube lumen, in combination with a core wire, provides a structure which can be used to advance the radiation source more safely. The distally sealed lumen through which the source travels prevents contamination with blood and is thus readily re-usable without sterilization. Further, the core wire constrains the movement of the tubular radiation source.